This invention generally relates to enclosures including multiple layers of flexible film, more particularly to multi-layered enclosures that laminate multiple sheets of film together into a single multi-layered enclosure suitable for use as a pouch or bag, and to the method of producing same. The multi-layered enclosures of this invention are particularly well suited for use as oversized or large capacity bags that are exceptionally tough yet provide superior fluid barrier properties.
In certain instances where film enclosures are utilized, it is especially important that the enclosures be not only exceptionally strong but also that they exhibit superior fluid barrier properties in order to attain a tough enclosure that provides an unusually long and stable shelf life. Substantial difficulties are encountered when attempting to combine these properties, particularly when they are to be provided in an oversized enclosure.
In the past, when attempting to produce multiple-layered enclosures in which two or more individually formed films are combined into a multi-layered enclosure, certain difficulties have been encountered. One difficulty is that the individual films must be sealed together at their edges, most typically by heat sealing devices. When used herein, the term "sealing" refers to bonding film layers together by a procedure that applies enough energy to the films so as to significantly alter the structure of the films. Typical energy sources include those that are thermal, ultrasonic and/or impulse. Thermal sealing, for example, typically utilizes a heated bar to transform thermoplastic films to their molten state to the extent that the molten material from one thermoplastic film combines with the molten portion of the other thermoplastic film to form a seal line having a thickness less than the combined thicknesses of the films prior to heating. Such reduced thickness weakens the overall strength of the films at the seal, and such strength deterioration is even more evident when one or more of the films is or includes a non-thermoplastic material that crystallizes when heated. On the whole, a material that has been heated to the point of crystallinity or that undergoes other significant changes in properties by the application of sealing-level energy thereto, loses much of its strength and pliability, and almost always is reduced in thickness.
When attempting to longitudinally seal such enclosures when they are unusually large or oversized, additional difficulties are caused by the excessive length of such longitudinal seals, often on the order of approximately six feet, which requires a very expensive sealing device having an oversized energy imparting fixture. A serious quality control problem is also presented because of the criticality involved in properly aligning the films on the fixture so that the seal is properly aligned and/or uniformly spaced from the edge of the enclosure and so that no gaps, buckles or folds are formed therealong. Additionally, forming transverse seals near the edge of a multiple part enclosure requires considerable care in alignment which is not conducive to high speed commercial production of such enclosures. Speed is further stifled because each enclosure must be individually aligned and sealed because the sealing fixtures are oriented transverse to the flow of the enclosures, rather than coincidental with the flow.
Also, films of the type that provide excellent fluid barrier properties, such as those that are coextruded with other tougher films, are relatively expensive when compared with tougher films that provide a less desirable fluid barrier. This means that there is an advantage to be gained in minimizing the use of these expensive fluid barrier films and in avoiding the often used approach of simply sealing such films together to provide the desired fluid barrier properties and strength.
These difficulties are brought under control by the present invention which combines the advantageous properties of film sheeting having excellent fluid barrier properties with blown film tubing that is exceptionally tough and relatively inexpensive, while combining the films in a manner that eliminates the need to form a longitudinal seal and that provides an enclosure having an integral, one-piece internal longitudinal wall, the invention including laminating together a sandwich of a film tubing between at least two film sheets.
It is accordingly a general object of this invention to provide an improved multi-layered enclosure.
Another object of the present invention is an improved multi-layered enclosure having both exceptional strength and excellent fluid barrier properties.
Another object of the present invention is to provide an improved oversized multi-layered enclosure that is free of side or longitudinal seals along the length thereof.
Another object of this invention is to provide an improved multi-layered enclosure, pouch or bag that is free of internal seams throughout the longitudinal extent or length thereof.
Another object of this invention is to provide an improved method for providing a tough and high fluid barrier multi-layered enclosure in a fast and continuous manner.